Zero-point adjustment of weighing device

ABSTRACT

A zero-point adjustment unit for a weighing device is comprised of a rough adjustment circuit, a fine adjustment circuit and a central processing unit. The central processing unit adjusts the zero-point of the weighing device by receiving a no-lead weight signal outputted from the weighing device and controls the output signals from the rough and fine adjustment circuits.

This is a division, of application Ser. No. 094,119 filed Sept. 4, 1987,U.S. Pat. No. 4,771,836 which was a division of Ser. No. 06/772,244,Sept. 3, 1985, U.S. Pat. No. 4,694,920.

This invention relates to zero-point adjustment of a weighing device andmore particularly to a zero-point adjustment unit for More particularly,it relates to a combinational weighing system having at least threemicrocomputers in its control unit for monitoring weight data, drivingthe means for delivering the articles to be weighed, performingcombinational computations and controlling the operation of the system.

Combinational weighing means weighing articles by a plurality ofweighing devices, performing arithmetic operations for combinations ofmeasured weight values and then selecting a combination according to apredetermined criterion. The major features of combinational weighingare great accuracy and high throughput. U.S. Pat. No. 4,398,612 issuedAug. 16, 1983 and assigned to the present assignee, for example,discloses an automatic weighing system of a combinational weighing typehaving a number of article batch handling units arrayed radially.Articles to be weighed are typically transported by a conveyor anddropped onto an article feeding unit which distributes them into theindividual article batch handling units. Weight-measuring meansassociated with the individual article batch handling units areelectrically connected to a control system such as a computer. Thecomputer not only computes combinations of weight values obtained fromthese weight-measuring means and selects a combination according to apredetermined criterion such as the combination which gives a totalweight that is within a preselected range, but also discharges thearticle batches from these selected article batch handling units forpackaging.

Systems according to the invention disclosed in U.S. Pat. No. 4,398,612such as Models CCW-201RLC and CCW-211RLC manufactured and sold by theassignee corporation have revealed the desirability of certainimprovements. Regarding their control units, in particular, it is founddesirable to generally improve the system flexibility and to introducesimpler methods of effecting zero-point and span adjustment on theweighing means. An easier input unit is also desirable by which even arelatively inexperienced user can operate the system in a variety ofmodes.

It is therefore an object of the present invention to provide acombinational weighing system with a control unit which is flexible andenjoys an increased degree of freedom in adjusting and controlling thissystem.

It is another object of the present invention to provide a combinationalweighing system with a control unit which allows the user to efficientlyperform zero-point and span adjustments of the weighing means in thesystem.

It is a further object of the present invention to provide acombinational weighing system with an input-output unit which enableseven a relatively inexperienced user to efficiently perform a greatvariety of available functions of the system without increasing theprobability of committing operational errors or necessitating the use ofan operational manual.

It is a still further object of the present invention to provide aninput-output unit for a combinational weighing system such that thescope of operation can be varied, depending on the qualification of theuser.

In general, the present invention provides a combinational weighingsystem of the type having a plurality of separate article batch handlingunits which are adapted to receive individual article batches, tomeasure their weights, to output analog weight signals and toselectively discharge the measured article batches in response to adischarge signal. Its control unit includes at least three centralprocessing units such as microcomputers individually forweight-monitoring, drive-controlling and combination computationpurposes. The weight-monitoring computer is adapted to receive theweight signals and to calculate and store batch weight values indicativeof the weights of the individual article batches. The drive-controlcomputer is adapted to receive an article batch discharge signal and tocause the article batch handling units to selectively discharge articlebatches according to the article batch discharge signal. Thecombinational computation computer is not only used for combinationalcomputation but is also adapted to control the overall operation of thesystem. The weight-monitoring part of the control system includescircuits for both rough and fine zero-point adjustment so that not onlyfine adjustment but also rough adjustment can be effected automatically.Span adjustment is also made easier by a method which provides a targetoutput value according to which an analog-to-digital converter isadjusted.

The accompanying drawings, which re incorporated in and form a part ofthe specification, illustrate one embodiment of the present inventionand, together with the description., serve to explain the principles ofthe In the drawings:

FIG. 1A-1C is a block diagram of a control unit according to onembodiment of the present invention for a combinational weighing system,

FIG. 2A-2G is a chart of the calculation computer in the control unit ofFIG. 1,

FIG. 3A-3E is chart of the weight-monitoring computer in the ocntrolunit of FIG. 1,

FIG. 4A-4I is a chart of the drive-control computer in the control unitof FIG. 1,

FIG. 5 is a drawing for explaining the principle of span adjustment, and

FIG. 6 is a schematic front view of a control panel.

FIG. 1 is a block diagram of a control unit according to one embodimentof the present invention for a combinational weighing system whichcomprises an article feeding means and a plurality (n-number) of articlebatch handling units, the article feeding means being adapted totransport articles to be weighed and to distribute them to theindividual article batch handling units as article batches, and eacharticle batch handling unit being adapted to receive, store, weigh anddischarge the delivered article batch and to output an analog weightsignal representing the measured weight value.

The control system according to this embodiment substantially consistsof three sections which will hereinafter be referred to as theweight-monitoring section, the main section and the drive-controlsection. These sections are indicated in FIG. 1 by arrows and one of theimportant features of the present invention is that each section has atleast one central processing unit (CPU) such as a microcomputer of itsown. This means that the control system according to this invention isof a multi-computer structure so that many adjustments and a greatvariety of operational modes can be made available.

The three most important CPUs according to the embodiment of FIG. 1 areindicated therein as CPU1, CPU2 and CPU3 belonging respectively to themain, weight-monitoring and drive-control sections. For the convenienceof subsequent explanations, they will also be referred to as the main(or calculation) computer, the weight-monitoring computer and thedrive-control computer, respectively. Explained briefly, theweight-monitoring computer CPU2 is adapted to monitor and store theweight information on the article batches from the article batchhandling units and the weight-monitoring section, cooperating with theweight-monitoring computer CPU2, not only receives weight value signalsand processes them to be stored but also performs zero-point adjustmentand span adjustment of the weighing devices; the drive-control computerCPU3 is adapted to output driving signals and the drive-control section,cooperating with the drive-control computer CPU3, not only drives theindividual article batch handling units selectively but also controlsthe feeding of articles thereinto; and the main computer CPU1 is adaptedto perform combinational computations to select a particular combinationof the article batch handling units according to the measured weightvalues outputted therefrom and also to generally control the operationof the weight-monitoring and drive-control computers CPU2 and CPU3, andthe main section, cooperating with the main computer CPU1 and includingtherein a remote control input-output unit to be described below, allowsthe user to control the operation of the entire system, for example, bychoosing a mode. Flow charts of these computers CPU1, CPU2 and CPU3 areshown in FIGS. 2, 3 and 4, respectively.

Each of the aforementioned computers CPU1, CPU2 and CPU3 has associatedtherewith a random access memory means. These memory means are indicatedin FIG. 1 respectively as MEMORY1, MEMORY2 and MEMORY3 (and as MEM1,etc. in the Figures). In what follows, the aforementioned three sectionswill be described one by one more in detail, starting with theweight-monitoring section.

As explained above, the weight-monitoring section is adapted to receiveanalog weight data (signal) from the article batch handling units and toprocess them for storage as digital data. In addition, this section isused for the zero-point adjustment and span adjustment of the weighingdevices in the article batch handling units. In FIG. 1, numerals 21-l. .. 21-n denote n weight-measuring devices such as load cells, each beinga part of one of the weighing devices in the article batch handlingunits. Numerals 22-l. . . 22-n denote n amplifiers each of which has itsinput side connected to the output terminal of the corresponding one ofthe weight-measuring devices 21-l. . . 21-n. The amplifiers 22-1. . .22-n produce respective amplified output signals indicative of theweight values obtained by the weighing devices. These amplified signalsare inputted through respective filters 23-l. . . 23-n to a multiplexer24 of a known type, comprising analog switches or the like, and aredelivered sequentially therefrom as output signals in response to aweight value read signal transmitted from the weight-monitoring computerCPU2.

The weight-monitoring section further includes two 8-bitdigital-to-analog converters 26 and 27 respectively for rough and finezero-point adjustment and a 14-bit digital-to-analog converter 28 forspan adjustment. These digital-to-analog converters 26, 27 and 28 willalso be referred to as DA1, DA2 and DA3 for convenience. In addition,there are three subtractors 31, 32 and 33 (or SUB1, SUB2 and SUB3)respectively for rough and fine zero-point adjustment and spanadjustment. The subtractor for rough zero-point adjustment 31 (or SUB1)is connected to the digital-to-analog converter 26 (or DA1) to receiveanalog signals outputted therefrom. Similarly, the subtractor for finezero-point adjustment 32 (or SUB2) is connected to the digital-to-analogconverter 27 (or DA2) to receive analog signals outputted therefrom. Aswill be explained later, the digital-to-analog converter and subtractorfor rough zero-point adjustment are so called because they are used forrough zero-point adjustment of the weighing devices and the circuit ofwhich they ar parts may be referred to as the rough zero-pointadjustment circuit. Similarly, the circuit of which thedigital-to-analog converter and subtractor for fine zero-pointadjustment are parts may be referred to as the fine zero-pointadjustment circuit and the circuit including the digital-to-analogconverter for span adjustment 28 (or DA3) and the subtractor for spanadjustment 33 (or SUB3) connected so as to receive analog signalsoutputted therefrom may be referred to as the span adjustment circuit.

On the output side, the multiplexer 24 is connected to the subtractorfor rough zero-point adjustment 31 which is connected to a rangeselector 35 on its output side. The range selector 35 is for selecting amaximum weight (range) allowed to be measured. As shown in FIG. 1, therange selector 35 is composed of a potential divider and a switch. Theswitch is adapted to be operated by a range selection signal RSSoutputted from the weight-monitoring computer CPU2 for selecting one oftwo choices UPPER RANGE and LOWER RANGE. UPPER RANGE is twice as wide asLOWER RANGE according to this embodiment. Signals outputted from therange selector 35 are inputted to the subtractor for fine zero-pointadjustment 32. On the output side, the subtractor for fine zero-pointadjustment 32 is connected to an analog-to-digital converter 40 throughtwo sample-and-hold circuits S&H1 and S&H2 which are connected inparallel, each having a switch on its output side. The weight-monitoringcomputer CPU2 is adapted to output a sample-and-hold signal S&H tooperate these switches substantially in synchronism with signals to themultiplexer 24 and to the analog-to-digital converter 40. Since there isan inverter means provided on the signal paths to one of thesample-and-hold circuits (S&H2 in FIG. 1), signals outputted from themultiplexer 24 (through the subtractors SUB1 and SUB2) are efficientlyprocessed in such a way that while a signal is being sampled by one ofthe sample-and-hold circuits, another signal is held in the other. Theadvantage of using two sample-and-hold circuits, therefore, is that theanalog-to-digital converter 40 can be more efficiently utilized becauseit generally takes several tens of microseconds to charge a circuitcapacitor for increasing the sampling accuracy and the analog-to-digitalconverter would not be functioning during such charging if only onesample-and-hold circuit were used. According to another embodiment,sample-and-hold circuits may be so arranged that two or more signalsfrom a weighing device are sampled before the multiplexer switches toanother weighing device.

Numeral 41 indicates a voltage level shifter, the purpose of which is tocreate a predetermined voltage ratio such as 128:1 between the voltagesinputted to the subtracters for zero-point adjustment 31 and 32corresponding to the input of the least significant bit. This being thepurpose of the level shifter 41, another voltage level shifting meansmay be inserted in the fine zero-point adjustment circuit to be usedeither in addition to or instead of the aforementioned voltage levelshifter 41.

The drive-control section, another of the three sections of which thecontrol unit of the present invention consists, is for driving thearticle feeding means and the article batch handling units in responseto a command which is received from the main computer CPU1 by thedrive-control computer CPU3 belonging to this section. FIG. 1 includes ablock diagram of the drive-control section of the present inventionaccording to on embodiment which is adapted to controllably drive acombinational weighing system of the type generally described in U.S.Pat. Nos. 4,494,619, 4,497,385 and 4,499,961 all assigned to the presentassignee. Explained more in detail, it will be assumed hereinafter notonly that the combinational weighing system under considerationcomprises an article feeding means and a plurality (n-number) of articlebatch handling units as described above but also that the articlefeeding means includes a vibratable dispersion feeder (abbreviated asDISP. FD.) and n independently vibratable radial feeders (abbreviated asRAD. FD.) such as troughs for the radially arrayed individual articlebatch handling units and that each article batch handling unit includesa pool hopper (abbreviated as P.H.) for receiving an article batch fromthe associated radial feeder, a weigh hopper (abbreviated as W.H.) forweighing the article batch discharged thereinto from the associated poolhopper. In addition, a timing hopper (abbreviated as T.H.) is alsoallowed to be a part of the system for receiving article batches fromthe weigh hoppers and discharging them in turn. The pool hoppers, weighhoppers and timing hopper are adapted to open and close at predeterminedtime intervals and the mechanisms for controlling the timing of theiropening and closing are referred to as pool hopper timers, weigh hoppertimers and timing hopper timer. The abbreviations shown above are usedextensively in the drawings and flow charts for convenience.

The drive-control section of this invention is characterized in that ncomputers 51-l. . . 51-n for controllably driving the individual articlebatch handling units are connected in parallel to the drive-controlcomputer CPU3 through interface means.

For convenience, these parallel-connected computers 51-l. . . 51-n willbe referred to as hopper driving computers. If the combinationalweighing system is of the type which employs a timing hopper as a partof an article collecting unit below the article batch handling units,the drive-control section may further include a timing hopper drivingcomputer 52 connected also in parallel with the aforementioned hopperdriving computers 51-l. . . 51-n.

These hopper driving computers 51-l. . . 51-n are individually connectedto hopper drivers 54-1. . . 54-n, each of which may typically includeclutches and brakes for controlling the motion of a pool hopper forreceiving an article batch and a weigh hopper for weighing it.Similarly, a timing hopper driver 55 for controlling the motion of thetiming hopper is connected to the timing hopper driving computer 52. Insuch a case, a signal to the packaging unit PU associated with thecombinational weighing system may be outputted from the timing hopperdriver 55. After packaging is done, the packaging unit PU outputs asignal which is delivered to the main computer CPU1 through thedrive-control computer CPU3 as will be described more in detail below.

The drive-control section of this embodiment also includes computers 56and 57 which are for controlling the vibration timing and intensity,respectively, of the dispersion and radial feeders. For the sake ofconvenience, they will be hereinafter referred to as the timing computerand intensity (or amplitude) computer, respectively. A dispersion feederdriver 58 for controlling the vibratory motion of the dispersion feederand n radial feeder drivers 59-l. . . 59-n for controlling the vibratorymotion of the radial feeders are connected both to the timing andintensity computers 56 and 57. Vibration intensity (or amplitude) ischanged by controlling the power to be supplied to the motor for causingthe vibration, and this is accomplished by using a zero cross detector60 to detect the zero-points of an AC power source and using a solidstate relay to switch on the motion with a predetermined delay after adetected zero cross point. In other words, the intensity computer 57controls the intensity of vibrations by regulating the delay between azero-point detected by the zero cross detector 60 and the switch-on timefor starting the vibratory motion.

The main section, the third of the three sections of which the controlunit of the present invention consists, includes the main computer CPU1and an input-output unit by means of which the user can select a mode ofoperation. As shown in FIG. 1, the input-output unit includes both inputmeans such as a keyboard (KEYS) and output means such as a displayer(DISPLAY) and a printer (PRINTER) in addition to a microcomputer forremote control (referred to as CPU4). Details of the input-output unitas well as a program for the remote control computer CPU4 will bedescribed after reference is made first to the flow charts of FIGS. 2, 3and 4 to explain how the three basic computers CPU1, CPU2 and CPU3 ofthe control unit perform their intended functions.

As can be seen in the main programs (MAIN) in these charts, theweight-monitoring computer CPU2 and the drive-control computer CPU3 areprogrammed to output a request signal RQ to the main computer CPU1 ("RQTO CPU1" in FIGS. 3 and 4) to solicit a command. When theweight-monitoring computer CPU2 sends this request signal afterinitializing and setting a flag for requesting initial data("INITIALIZE" in FIG. 3), the main computer CPU1 outputs to theweight-monitoring computer CPU2 a bus request signal BUSRQ to requestthat the necessary bus line be opened ("BUSRQ ON TO CPU2" in FIG. 2).When the bus request signal BUSRQ is received, the weight-monitoringcomputer CPU2 automatically sets a tristate logic device in ahigh-impedance state to activate a bus acknowledge signal BUSAK, therebyinforming the main computer CPU1 that the required bus line has beenopened. When the bus acknowledge signal BUSAK is detected ("BUSAK?" inFIG. 2), the main computer CPU1 checks whether the weight-monitoringcomputer CPU2 is requesting initial data and, if a flag for requestinginitial data is detected, transfers the initial data from MEMORY1 toMEMORY2 ("TRANSF. INITIAL DATA FROM MEM1 TO MEM2"). Subsequently, the RQsignal from the weight-monitoring computer CPU2 is reset ("RESET RQ" inFIG. 2) and a signal is outputted to the weight-monitoring computer CPU2to release (cancel) the bus request ("BUSRQ OFF TO CPU2"). When thelatter signal is received, the weight-monitoring computer CPU2 releasesthe BUSAK signal and automatically resumes the processing of itsprogram, checking whether the initial data have been received.("RECEIVED DATA? "). If initial data have been set in MEMORY2, theweight-monitoring computer CPU2 checks whether a command to read anoutput from the analog-to-digital converter 40 has been set ("A/D READCOMMAND" in FIG. 3). This command, however, is not set by the maincomputer CPU1 but by an interrupt signal outputted periodically from anindependent timer at a fixed frequency. Thus, the program according tothe subroutine SCLIN is adapted to be repeated periodically at a fixedfrequency in order to constantly update the weight information from theweighing devices 21-1 . . . 21-n as will be explained below. Bycontrast, "manual zero", "auto zero", "span" and "change mode" commandsare set by the main computer CPU1. As shown in FIG. 2, these commandsare inputted to the weight-monitoring computer CPU2 by exchangingaforementioned signals BUSRQ and BUSAK between the two computers and bywriting these commands in MEMORY2. Thus, the BUSRQ signal from the maincomputer CPU1 functions as a kind of interrupt signal. Similarly, if theinput data transferred from the remote control computer CPU4 to the maincomputer CPU1 are for modifying the initial data, a change mode commandis set to the weight-monitoring computer CPU2 in the same manner asexplained above. When the weight-monitoring computer CPU2 finds that achange mode command has been set ("CHANGE MODE COMMAND" in FIG. 3), itresets the command, sets a flag to request new data ("RESET CHANGE MODECOMMAND. REQUEST INITIAL DATA") and returns to the beginning of the MAINprogram.

The subroutine SCLIN (=scale data in), as shown in FIG. 3 for a systemwith fourteen article batch handling units, substantially consists of aloop (returning from the point "D"), each cycle relating to one of theweighing devices in the individual article batch handling units. Whenthe SCLIN is called, the aforementioned command to read the outputs fromthe analog-to-digital converter 40 is reset ("RESET A/D COMMAND") and asignal RSS explained above and shown in FIG. 1 is outputted to the rangeselector 35 to select one of the available ranges ("OUTPUT RSS"). Next,the multiplexer input port number n (a dummy index in this case, not thenumber of article batch handling units in the system) is set to 1, orthe "first" weighing device to be considered in the aforementioned loopis specified ("n=1" and "MULTIPLEXER=n") so that the multiplexer 24 willoutput the weight signal from the "first" weighing device.

Next, a zero atum (or a zero-point adjustment preset value ZD_(n)related to the nth weighing device, to be explained more fully later inconnection with the subroutine ZERO, is inputted to thedigital-to-analog converters for zero-point adjustment DA1 and DA2 and aspan datum (or space adjustment preset value) SD_(n) related to the nthweighing device and to be explained more fully later in connection withthe subroutine SPAN, is inputted to the digital-to-analog converter forspan adjustment DA3. Both ZD_(n) and SD_(n) are digital values andstored in MEMORY2. Thereafter, a signal S&H is outputted to thesample-and-hold circuits ("SET S&H") and a starting signal is sent tothe analog-to-digital converter 40 ("START TO A/D CONV") to start thefirst cycle of the aforementioned loop. The S&H signal is for selectingone of the two sample-and-hold circuits to sample while the other holdswhen it is set. When it is reset, the two sample-and-hold circuitsexchange their holes, the sampling circuit beginning to hold and theholding circuit beginning to sample. As explained above, the setting andresetting of the sample-and-hold circuits are carried out in synchronismwith the sending of a starting signal to the analog-to-digital converter40 and reading an output therefrom. These three steps are sometimescombined in FIG. 3 and denoted as "A/D DATA IN".

Because fluctuations are inevitable in measurements, the subroutineSCLIN does not rely on a single reading but allows the user to choosewhether 2 or 4 output data from the analog-to-digital converter 40should be considered to obtain an average value D_(ave). Inside theaforementioned loop, a first of these 2 or 4 output data is read ("READA/D OUTPUT1") and stored in D_(sum) ("D_(sum) =OUTPUT1"). In preparationfor the input of the next output datum, a reset signal is sent to thesample-and-hold circuits and a start signal to the analog-to-digitalconverter 40 in synchronism. The information whether 2 or 4 output datashould be considered to calculate an average is one of the initial datamentioned above. If the answer to the question "2 TIMES?" is "NO", itmeans that 4 output data are considered to calculate the average valueand the weight-monitoring computer CPU2 proceeds to read a second outputdatum for the analog-to-digital converter 40 ("READ A/D OUTPUT2") andadds this value to that of the first output datum now stored in D_(sum),the sum being re-stored in D_(sum) ("D_(sum) =D_(sum) +OUTPUT2"). Asimilar step including setting or resetting of the sample-and-holdcircuit and starting of the analog-to-digital converter 40 is repeatedto read a third output and a fourth output and add them to the sum inD_(sum). If the answer to the question "2 TIMES?" is "YES", only twooutputs are added in D_(sum). The value stored in D_(sum) issubsequently divided by 2 once (if the response to "2 TIMES?" is "YES")or twice (if this response is "NO") to obtain a desired average valueD_(ave).

In the subsequent several steps, the weight-monitoring computer CPU2examines if the fluctuation in this measured value is converging or not.For this purpose, the value of D_(ave),n (the value of D_(ave) for thenth weighing device) obtained previously is read from MEMORY2 and set asP_(ave) also ("PREVIOUS D_(ave),n TO P_(ave) ") and a predeterminedmaximum allowable deviation (inputted originally as one of the initialdata) is inputted as D_(dev) ("D_(dev) =DEVIATION VALUE"). If theabsolute value of the difference between P_(ave) and D_(ave) is notsmaller than D_(dev), the newly derived value D_(ave) is stored asD_(ave),n ("D_(ave),n =D_(ave) ") for use in the subsequent steps. Ifotherwise, a three-to-one weighed average between P_(ave) and D_(ave) isstored instead as D_(ave),n. This is to give more weight to thepreviously stored value (or to find the previously stored value moretrustworthy) if the new value deviates from it significantly.

Thereafter, an appropriate flag is set according to the value ofD_(ave),n The under flag, over flag, minus flag, empty flag andstability flag are initially reset. The under flag is set if D_(ave),n=0, and the over flag is set if D_(ave),n is greater than apredetermined maximum value. At this stage, the dummy index n isreplaced by n+1 ("n=n+1"), the multiplexer is addressed to the newly setvalue n, and the zero-point and span adjustment preset values addressedto the new (previously (n+1)st and now the nth) weighing device arerespectively inputted to the digital-to-analog converters for zero-pointand span adjustments, respectively, as done before at the beginning ofthis subroutine. The reason for entering these values for the nextweighing device at this point rather than at the end of this loop isthat it generally takes a relatively long time to read and input thesedata.

Thereafter, accordingly, the value D_(ave),n obtained immediately abovemust be referred as D_(ave),n-1 and the minus flag is set if a storedoutput value from the analog-to-digital converter 40 at the previouszero-point adjustment (Dzero to be explained in detail later inconnection with the subroutine ZERO) is subtracted from D_(ave),n-1 toobtain a net weight value NET_(n-1) and if this value is negative. Theempty flag is set if NET_(n-1) is smaller than the empty weight

In the subsequent few steps, the net weight value NET_(n-1) isnormalized by dividing or multiplying it by an appropriate normalizationfactor to obtain a weight value W_(n-1). For example, if 10 digitalcounts correspond to 5g, the NET value might be divided by 2("Wn-1=NETn-1/2"). Since the normalization factor depends on how therange selector 35 has been set, a question is asked which of the choiceshas been made ("UPPER RANGE?"). If 10 digital counts actually turn outto correspond to 2.5 g, the value of W_(n-1) obtained above must bedivided further by 2 ("Wn-1=Wn-1/2") to obtain a correct weight valueW_(n-1).

At this point, the weight-monitoring computer CPU2 determines whetherthe fluctuation in the weight data from this weighing device hasstabilized. For this purpose, the previously stored value of D_(ave),n-1is taken out of MEMORY2 as P_(ave),n-1 and the absolute value of thedifference between P_(ave),n-1 and D_(ave),n-1 is computed and definedas DIF. If DIF is not smaller than a predetermined stability range SR,the stability flag is not set. If DIF is smaller than SR, it isconsidered that stability has been established. The user is required todecide initially whether a single comparison of D_(ave),n-1 withP_(ave),n-1 is sufficient to establish stability or a further comparisonwith a penultimate stored average value P'_(ave),n-1 is required. Thisinformation (entered as initial data) is checked ("TWICE COMPARISONMODE?") and D_(ave),n-1 is accordingly compared only once withP_(ave),n-1 or twice with P_(ave),n-1 and P'_(ave),n-1. The stabilityflag is set if stability is deemed to have been established by eithercriterion. At the end, a set signal is sent to the sample-and-holdcircuits and a start signal is outputted to the analog-to-digitalconverter 40 to close the loop. This loop is repeated as many times asthe number of weighing devices or article batch handling units in thesystem.

The subroutine ZERO is called as explained above by a manual zerocommand or an auto zero command. Thus, the zero-point adjustment can beeffected either on only one of the weighing devices by specifying theparticular one or on all of them. Before reference is made to the flowchart of FIG. 3, the mechanism of zero-point adjustment according tothis invention will be briefly outlined.

To perform a zero-point adjustment, the weighing device of interest iskept unloaded and the no-load weight value signal is introduced throughthe multiplexer 24 to the subtracter SUB1. Next, a 16-bit digital valuepreviously stored as ZD_(n) (corresponding to the nth weighing deviceunder consideration) is fetched from MEMORY2 and its first (top orhigher) 8 bits are inputted into the digital-to-analog converter forrough adjustment DA1 and the second (bottom or lower) 8 bits into thedigital-to-analog converter for fine adjustment DA2. Similarly, a 14-bitdigital value stored in MEMORY2 as SD_(n) which is one-half of themaximum that can be inputted to the digital-to-analog converter for spanadjustment 28 is inputted thereto. Since the digital-to-analog converterfor span adjustment 28 is a 14-bit converter, the maximum value that canbe inputted has 1 in every bit and the value inputted thereto in thisstep therefore has 1 only in the first (top or maximum) bit, all theother bits having 0. The output voltage from the digital-to-analogconverter DA1 is also inputted to the subtracter SUB1 and the differencevoltage signal outputted therefrom is inputted to the next subtractorSUB2 for fine adjustment. For the sake of explanation, let ushereinafter consider the mode of operation for which the range selector35 does not cause any level shift in voltage and that the level shifter41 is so set that the output voltage from the digital-to-analogconverter DA2 per bit thereof, when entering the subtracter SUB2 forfine adjustment, will be 1/128 of that from the digital-to-analogconverter DA1 when entering the subtracter SUB1 for rough adjustment.The output from the subtracter SUB2 is passed through thesample-and-hold circuits and the analog-to-digital converter 40 and isinputted to the weight-monitoring computer CPU2. This input signal isstored in MEMORY2 as the zero-point of this weighing device.

The level shifter 41 may be so set that the aforementioned ratio inper-bit output voltage will be 2⁸ =256 instead of 128. It is preferable,however, to adjust the level shifter 41 and the range selector 35 (aswell as any extra voltage shifter which may be inserted between thedigital-to-analog converter DA2 and the subtracter SUB2 as mentionedbefore) in such a manner that the ratio of minimum controllable voltages(corresponding to the least significant bits) by the two zero-pointadjustment digital-to-analog converters DA1 and DA2 will be 2⁷ ratherthan 2⁸. The reason for this preference, as will become easier tounderstand later, is that the maximum error that can be detected by thedigital-to-analog converter DA2 for fine adjustment increases by afactor of 2, and this will prove to be a significant advantage when thesystem is operated in a mode wherein rough adjustment is omitted.

Reference being now made to the flow chart of the subroutine ZERO inFIG. 3, the mechanism of zero-point adjustment outlined above will beexplained more in detail. After the head number n (a dummy index) isspecified ("HEAD NO. n") and the multiplexer 24 is told to output theno-load weight signal corresponding to this weighing device("MULTIPLEXER=n"), the aforementioned initial values ZD_(n) and SD_(n)are inputted to the digital-to-analog converters DA1, DA2 and DA3.

Since there is a total of 16 bits between the digital-to-analogconverters for zero-point adjustment DA1 and DA2, the routine fordetermining the zero-point essentially consists of a 16-cycle loop. Inpreparation for this loop, a dummy variable j is set to 16 and ZD_(n) to0 ("ZDn=0, j=16"). Let us now define B₁ and B₂ each as an 8-bit numberentered in the digital-to-analog converters DA1 and DA2, respectively, a16-bit number B (representing ZD_(n)) being therefore defined as thathaving B₁ and B₂ as its top and bottom 8 bits. At the start of thisloop, B (=ZD_(n)) is zero and hence both B₁ and B₂ are zero.

In the first step inside the loop, the weight-monitoring computer CPU2outputs (B+2^(j-1)) to the digital-to-analog converters DA1 and DA2. Inthe first cycle, therefore, the inputted 8-bit values are B₁ =(10000000)and B₂ =(00000000). The digital value Z_(n) which is then outputted fromthe analog-to-digital converter 40 is compared with a reference zerovalue Z_(ref) stored in MEMORY2 ("Z'_(n) <Z_(ref) ?"). If Z' is not lessthan Z_(ref), B is replaced by (B+2^(j-1)) and j by (j-1). Since B waszero and j equaled 16 at the beginning of the first cycle, B=2¹⁵=(1000000000000000) and j=15 at the end of the first cycle. If Z' wasless than Z_(ref) in the first cycle, the aforementioned replacing stepis skipped and B remains zero at the end of the first cycle.

This loop is repeated thereafter until j becomes zero ("j=0?"). If thevalue of ZD_(n) at the end of the loop is zero or exceeds a certainmaximum value ("ZD_(n) =0?" and "ZD_(n) =MAX?"), a zero error flag isset, a request signal RQ is outputted to the main computer CPU1 for thenext command and the subroutine comes to an end. Otherwise, the top 8bits of the binary code B is stored as the bias value for roughzero-point adjustment for this weighing device, the bottom 8 bitslikewise for fine adjustment ("STORE ZDn AS NEW PRESET ZDn"), and theoutput weight value D_(zero) from the analog-to-digital converter 40 atthis point ("D_(zero) =A/D OUTPUT") is stored as the new zero-point("STORE D_(zero) AS NEW ZERO A/D VALUE"). A flag is set to indicate thecompletion of the zero-point adjustment ("SET COMPLETION FLAG FOR ZEROADJUSTMENT") and the subroutine ends.

One of the characteristics of the control unit of the present inventionis that its weight-monitoring section includes separatedigital-to-analog converters DA1 and DA2 for rough and fine zero-pointadjustments.

When the initial loads of the weighing devices are nearly equal as isoften the case, however, it is usually not necessary to repeat theentire zero-point adjustment process on all weighing devices. Instead,it may be sufficient to carry out both rough and fine adjustments ononly one of the weighing devices.

After the bias value B₁ for rough adjustment is obtained by theadjustment of this one weighing device, this value may be used for theother devices so that only fine adjustments need to be done on theremaining weighing devices. A flow chart (not shown) for a situationlike this where only zero drifts need be corrected and rough adjustmentsare not necessary may look similar to that of the subroutine ZEROdescribed above, but the comparable loop need be repeated only 8 timesbecause only the bottom part B₂ of the binary code is considered and thebias value B₁ for rough adjustment need not be outputted.

The aforementioned advantage of setting the voltage ratio from thezero-point adjustment digital-to-analog converters DA1 and DA2 to be 2⁷rather than 2⁸ becomes apparent at this point. An increase of this ratiofrom 2⁷ to 2⁸ means that the largest error that can be corrected by thefine adjustment routine like this becomes bigger by a factor of 2.

A further characteristic of the control unit according to the presentinvention is that the entire zero-point adjustment circuit includingboth rough and fine adjustments is put behind the multiplexer 24 so thatthe number of component parts is significantly reduced. Moreover, sinceboth rough and fine adjustments can be carried out automatically andsimultaneously by a computer, zero-point adjustment becomes easier andfaster. This should in fact be contrasted with conventional zero-pointadjustment circuits which, although called "automatic", are onlypartially automatic. According to typical examples, what is referred toabove as rough adjustment is usually carried out by manually operatingvariable resisters for adjustment. Since a combinational weighing systemtypically includes 10 through 15 weighing devices to be zero-adjusted,such manual rough adjustment was a cumbersome procedure.

The subroutine SPAN is called by a span command as explained above. Aspan adjustment means an adjustment made in such a way that, when ananalog signal representing a weight value obtained by a weighing deviceis converted into a digital signal, this digital signal will correspondto a value by which the user wishes to represent the actual weight ofthe weighed load. Assume, for example, that the user wants a load of 100g to be represented by a digital value of 1000, but an unadjustedcontrol system converts a weight signal corresponding to 100g into adigital signal of 1010. In such a case, it is necessary to effect anadjustment in such a manner that the digital output value is changedfrom 1010 to 1000. This step is called a span adjustment.

The conventional method of span adjustment involved a repetition ofadjustments until convergence could be obtained. This is explained morein detail in FIG. 5, wherein W_(O) and W_(T) respectively denote theweight values when a weighing device under consideration is unloaded andwhen it is carrying a standard weight, the difference (W_(T) -W.sub.))thus representing the effect of the standard weight. According to theconventional method, an unadjusted span is determined first by obtainingoutputs N₀ and N (corresponding to D_(zero) and S_(n), respectively)from an analog-to-digital converter respectively when the weighingdevice is unloaded and when it is loaded, the difference N-N₀ being theunadjusted span. In order to obtain a desired span N_(S) (correspondingto S_(ref) in FIG. 3), the conventional method was to adjust theanalog-to-digital converter so that the output therefrom with thestandard weight thereon will change from N to a new value N'_(c) suchthat N'_(c) -N₀ =N_(S). With the aforementioned adjustment of theanalog-to-digital converter, however, its zero-point also shifts, say,to N'_(c0). Thus, the span does not change from the original unadjustedvalue N-N₀ to the desired span value N_(S) but to a new span valueN'_(c) -N'_(c0) which, though closer to N_(S) than the aforementionedunadjusted span, is not equal to N_(S). It is necessary therefore torepeat this process until conversion is obtained.

The span adjustment program according to the present invention, bycontrast, does not require the standard weight to be placed on and takenoff the weighing device many times until conversion is obtained. Asexplained above, if the analog-to-digital converter is adjusted so thatthe output changes from N to N' and the no-load output changes from N₀to N'₀, the straight line defined by the points W₀, N'₀) and (W_(T), N')in the graph of FIG. 5 will pass the origin because of theproportionality relationship between the weight value and the converteroutput. Since the new span is N'-N'₀ and the purpose of span adjustmentis to make it equal to N_(S) rather than N'-N₀ =N_(S), we can derivefrom the relationships between similar triangles formed in FIG. 5 thatN'=N_(S) N/(N-N₀) and N'_(0=N) ₀ N_(S) /(N-N₀). The method of spanadjustment according to the present invention can therefore besummarized as follows.

The reference voltage to the analog-to-digital converter 40 is set atits lowest possible value and the output D_(zero) therefrom is read whenthe weighing device of interest is free of a load. Next, a standardweight is added and the output S_(n) is read. A desired span valueS_(ref) is assumed to be predetermined and stored. These three valuesuniquely determine S_(target=S) _(n) S_(ref) /(S_(n) -D_(zero)) andD'_(zero) =D_(zero) S_(ref) /(S_(n) -D_(zero)) as above. With thestandard weight still kept on the weighing device, the span adjustmentdigital-to-analog converter DA3 is adjusted by a well-known sequentialcomparison-type analog-to-digital conversion method until the outputfrom the analog-to-digital converter 40 reaches the value S_(target).After the span adjustment is completed, the previously stored zero-pointvalue D_(zero) is corrected (updated) to D'_(zero).

Span adjustment is carried out after zero-adjustments of all weighingdevices have been completed. This may be accomplished either by placinga standard weight on each weighing device sequentially to span-adjustone device at a time or by placing standard weights on all weighingdevices so that they can all e adjusted automatically.

The subroutine SPAN of FIG. 3 is called by a span command as explainedabove. For the span adjustment of the nth weighing device ("HEAD NUMBER=n"), preset values ZD_(n) and SD_(n) are inputted to thedigital-to-analog converters as in the subroutine ZERO. Since the spanadjustment is carried out after zero-point adjustments of all weighingdevices, this means that the digital zero-bias values determined by thezero-point adjustment process are outputted to the digital-to-analogconverters for zero adjustment 26 and 27. With the standard weightcarried by the weighing device of interest (the nth), signals are sentto the sample-and-hold circuits and to the analog-to-digital converter40 ("A/D DATA IN") and the target output S_(target) is calculated by theformula described above. In this calculation, the value of D_(zero)obtained in the previous-point adjustment process and stored in MEMORY2is directly utilized.

After S_(target) is calculated, the following several steps are fordetermining a digital value SD_(n) corresponding to the voltagenecessary for the desired span, or that digital value which, wheninputted to the digital-to-analog converter for span adjustment DA3,will cause the analog-to-digital converter 40 to output the desireddigital value S_(target). This is done by a sequential comparisonroutine described above in connection with the subroutine ZERO. Sincethe digital-to-analog converter for span adjustment DA3 is a 14-bitconverter, it is carried out in this situation by means of a 14-cycleloop (from "j=14"to "j=0?"). As done in the subroutine ZERO, a spanerror flag is set if the value SD_(n) thus obtained is zero or exceeds apredetermined maximum value. Otherwise, a completion flag is set, thespan command is reset and the subroutine ends after a request signal RQis outputted to the main computer CPU1 to solicit a next command.

The drive-control computer CPU3 is adapted to keep monitoring theconditions of the hoppers and feeders ("T.H. CONTROL", "W.H. CONTROL","P.H. CONTROL" and "FD. CONTROL") and, like the weight-monitoringcomputer CPU2, outputs a request signal RQ to the main computer CPU1("RQ TO CPU1") to solicit a command, causing an exchange of signalsBUSRQ and BUSAK. Actual motion of the hoppers, however, is controlled bythe hopper driving CPUs 51-l. . . 51-n and 52 each of which is assignedan identification switch (which may be a 4-bit switch if the number ofarticle batch handling units in the system is 14 as in the embodimentwhich has been in consideration) and each hopper operating signaloutputted from the drive-control compute CPU3 includes a message foridentifying the hopper driving computer to which it is addressed. Whenone of the hopper driving computers recognizes that the outputtedmessage is addressed to itself, it accepts the message and causes theassociated driver 54-l. . . 54-n or 55 to function according to themessage. In other words, these hopper driving CPUs 51-l. . . 51-n and 52keep monitoring the conditions of the hoppers and the message from thedrive-control computer CPU3 functions as an interrupt. This mode ofoperation is quicker than if it were done by a command.

There are timers provided to hoppers and feeders (such as weigh hoppertimer) so that the radial feeder and hoppers associated with eacharticle batch handling unit are sequentially driven according to apredetermined timing schedule. Such timing schedule can be adjusted byan input from the input-output unit as will be explained below.According to one embodiment of the invention, furthermore, the hoppersto be driven may be divided into three groups (partitions) so that thehoppers belonging to different groups will have different timingschedules in such a way that they do not discharge simultaneously. Thisis to reduce the adverse effects of collisions among article batchesbeing discharged into the timing hopper or a collecting chute. This modeof operation is referred to as the stagger dump mode in FIG. 4.

When the main (calculation) computer CPU1 completes a combinationalcomputation and selects a particular combination of article batchhandling units, the selection is communicated to the drive-controlcomputer CPU3 so that the hoppers and radial feeders associated with thearticle batch handling units in the selected combination are activatedaccording to the timing schedule explained above. The drive-controlcomputer CPU3 also participates in adjusting the vibrations (intensityand timing) of the feeders in accordance with inputs from theinput-output unit.

The main computer CPU1 is programmed to carry out combinationalcalculation and to generally control the operation of the system. Dataand commands inputted by the user and signals soliciting the user'scommand are communicated through this computer. Methods of combinationalcalculation have been known and incorporated in many automatic weighingmachines such as aforementioned Models CCW-201RLC and CCW-211RLC of theassignee corporation. Detailed explanation of FIG. 2 is thereforeomitted.

As recited above, one of the objects of the present invention related toa combinational weighing system is to provide an input-output unit whichis easy to operate. This object is attained in one aspect by providing aremote control computer CPU4 which is programmed, as will be explainedin detail below, so that even a relatively inexperienced user canoperate the system easily. In another aspect, various input and outputmeans shown in FIG. 1 such as the printer PRINTER, the displayer (suchas a plasma display panel) DISPLAY and a control panel including thekeyboard (KEYS) are built in a unitized structure (not shown).

FIG. 6 is a front view of the control panel schematically drawnaccording to one embodiment of the present invention, characterized inthat it includes only a relatively small number of keys. The ON and OFFkeys are for switching power on and off. The START key is used not onlyfor starting zero-point and span adjustments, the printer PRINTER, etc.but also for specifying certain items to be inputted to the maincomputer CPU1. The STOP key is used not only for stopping the operation,printing, etc. but also for changing the display mode back to theinitial menu (to be explained below). The DISP key is used for changingthe display mode to a print display mode. The ON LINE/OFF LINE key isused for placing the entire operation under the control of a hostcomputer and disconnecting such a connection with a host computer.During an ON LINE period, the other keys cannot be operated. The UP andDOWN keys indicated by upward and downward pointing arrows are formoving a cursor up and down on the display panel. The number keys 0-9are for inputting numerical values. The CLEAR (C) key is for clearing anumerical entry. The SET key is used not only for inputting the valueset by the number keys into the computer memory but also for shiftingthe cursor to the next set item.

The basic function of the remote control computer CPU4 is to allow theuser to communicate with the system via the main computer CPU1. In orderto make the operation of the system easy and simple, the remote controlcomputer CPU4 is so programmed that the user can input commands and datainteractively. In other words, the remote control computer CPU4 isprogrammed to display various menus and a curser which the user canfreely move on the display screen (which may be a plasma display panelas mentioned above or alternatively a cathode ray tube) by handling someof the aforementioned keys (or buttons). According to one embodiment,the display holds up to eight lines of information and the cursor is ablinking square, indicating an item with respect to which an input isinvited. For menus which are longer than eight lines, the first eightlines are displayed initially. The remaining lines can be displayed byfirst pressing the DOWN key to move the cursor to the bottom of thedisplay. Then, the display can be scrolled up one line at a time byfurther pressing the DOWN key. The display returns to the first line ofthe menu if it is scrolled up past the last line of the menu. Thescrolling feature also works in reverse: if the UP key is pressed whenthe cursor is on the first line, the display is changed to the last menuline. The display is also adapted for various messages to guide theuser. An audio alarm (buzzer) is adapted to sound if an incorrect key ispressed.

A further object of the present invention related to a combinationalweighing system is to provide a means whereby the scope of operationthereof can be varied, depending on the qualification of the user.According to one embodiment of the present invention which will bedescribed in detail hereinafter, the program for the remote controlcomputer CPU4 is so structured that the users are classified into threelevels according to the scope within which they are allowed to operatethe system. Level 1 is for general users, Level 2 includes supervisorsand Level 3 is for engineers with special knowledge of the system. Thenumber of items that can be selected from a menu increases as the levelof the user becomes higher. The total number of items is 10 and they aredisplayed together with date and time after the power is switched on anda title display is made for a brief moment such as three seconds. Thefirst three of these items are considered Level 1 items and the nextfive items are Level 2 items. The final two items are Level 3 items.These 10 items will be briefly explained below.

The first item is titled "Zero-Adjustment". Zero-point adjustment can beeffected either on all weighing devices or only on a specified one,depending on how a message (numerical value) is inputted. When only theitems of Level 1 are displayed, the display can be changed to that ofLevel 2 or Level 3 by entering a code word. Such a code word issometimes referred to as the password or the keyword. These two wordsare often used interchangeably.

The second item is titled "Production" which is for starting a normalweighing process. The product name and target weight W_(T) are displayedwhen the choice is inputted by a code number. The third item is titled"System Draining" which is used to discharge the articles remaining inthe apparatus either when the articles being weighed are to be changedor at the end of the day.

The fourth item is titled "Function". This step is used to set the date,time, feed control, weight control and calculation mode by moving thecursor to the corresponding sub-item in the "Function Menu"which isdisplayed as soon as "Function" is selected. The feed control is todetermine whether the vibration intensity and timing of the dispersionand radial feeders should be controlled automatically or manually.Manual control should be selected if automatic control does not workproperly, for example, in the case of sticky products. The weightcontrol is to specify how a combination of article batch handling unitsshould be selected. The selection may be in terms only of a minimumweight so that the total weight of the article batches in the selectedcombination should be equal to or greater than a specified target value.Alternatively, it may be required additionally that the total weight inthe combination must not exceed a certain upper limit W_(up). Thecalculation mode specifies whether combinational calculations may becarried out for a second time if a combination satisfying the conditionsfor selection was not obtained in the first attempt.

The fifth item is titled "Calculation" and is used as a verification anddiagnostic tool by displaying the selected weighing devices and theweight values from each.

The sixth item is titled "Prearrangement" and is used to set any of theitems which becomes displayed in a "Prearrangement Menu". Among the manyitems that can be set in this step are the target weight to bedischarged to the packaging unit PU, the maximum upward deviation fromthe target weight, the vibration intensity and interval between startingtimes of dispersion and radial feeders, the number of times (dump count)which the articles will be discharged from the system to deliver thetarget weight, the product name to be entered by a numbered letter code(such as "10" representing "A" and "11" representing "B"), etc.

The seventh item is titled "Span Adjustment" and is for performing spanadjustment. A selection is made whether all weighing devices or only asingle weighing device should be adjusted. After the START key ispressed, the display returns to the initial menu if no error occurs.There is no need to press the STOP key.

The eighth item is titled "Adjustment" and is for setting any of thesub-items in the "Adjustment Menu"which is displayed. Among the manysuch sub-items are the specification of article batch handling units tobe deactivated, the setting of various delay times such as the timeinterval between the opening of a weigh hopper and that of theassociated pool hopper.

The ninth and tenth items are for adjustments to be made only by trainedengineers.

In summary, the input/output unit of the present invention for acombinational weighing apparatus is compact but versatile. It is compactbecause the numbers of keys on the control panel is very limited in viewof the great variety of adjustments and mode settings that can beachieved therefrom and further because both a display means and aprinter means can be built into a unitized structure with the controlpanel. It is versatile because it is easy to operate and yet can performa large variety of functions. This is a particularly significantadvantage achieved by this invention because, as stated at the outset,the major purpose of using a set of three microcomputers to perform thebasic functions of a combinational weighing system was to gainflexibility by carrying out most of the adjustments and mode settings bysoftware. As flexibility is gained and a larger variety of optionsbecomes available, simplicity of operation becomes even more desirablethan before.

The system operation is made easy firstly because different types ofcontrols and adjustments which used to be carried out at different partsof the system can now be performed from one centralized location andsecondly because a menu formalism has been adopted so that the user,even if relatively inexperienced, can interactively operate the systemby reading instructions which appear as messages in the display meansand proceed by choosing items from available options by moving a cursorand operating only a few keys. Its versatile aspects include thecapacity of allowing access to different sets of options, depending onthe status of the user, simply by defining security codes such as apassword and a keyword.

This invention has been described above in terms of only a limitednumber of embodiments, but the description given above is intended to beinterpreted as illustrative rather than as limiting. Many changes andmodifications can obviously be made within the spirit of this invention.For example, the combinational weighing system of this invention neednot include a timing hopper to collect the article batches dischargedfrom weigh hoppers. Models with a simple collecting chute instead of atiming hopper have been commercially available and a control unitdisclosed in FIG. 1 can be made adaptable to such models by removing thetiming hopper driving CPU 52 and the timing hopper driver 55. Similarly,the control unit of FIG. 1 can be made adaptable to a combinationalweighing system having article batch handling units installed in aside-by-side relationship among themselves rather than in a circularconfiguration and hence having feeders which are different from thedispersion and radial feeders considered in the embodiments illustratedabove.

As for the circuits for zero-point adjustment, it is not necessary asshown in FIG. 1 to provide two circuits separately for rough and fineadjustments. Although it is more economical to provide two 8-bitconverters as in the illustrated embodiment than to use one 16-bitconverter, the rough and fine zero-point adjustment circuits of thepresent invention may be combined into a single circuit with onedigital-to-analog converter and one subtracter. Such an alternativeembodiment has the advantage of reducing the number of constituentcomponents in the circuit.

As already mentioned, furthermore, the level shifter 41 in theweight-monitoring section may be replaced by a voltage divider insertedbetween the digital-to-analog converter for fine zero-point adjustment27 and the subtracter for fine zero-point adjustment 32.

As for the combinational computations, a great variety of computerprograms have been available and incorporated into prior artcombinational weighing systems using only one central processing unit.They include programs which calculate all combinations of all articlebatch handling units in every cycle, those which calculate combinationsonly from some (not all) of the article batch handling units, forexample, by excluding for a specified number of cycles those articlebatch handling units which have once been selected in a combination,those which select a combination providing the smallest total weightequal to or greater than a given target weight, those which can selectany combination providing a total weight within a specified interval,etc. The flow chart of the main computer CPU1 in FIG. 2 is useable forall these programs either directly or with only minor changes which canbe effected by any person skilled in the art of programming.

In short, the description given hereinabove is intended to be construedbroadly and all changes and modifications which should be apparent to aperson skilled in the art such as those variations illustrated above areto be considered within the scope of this invention.

What is claimed is:
 1. A zero-point adjustment unit for a weighingdevice comprisinga rough adjustment circuit, a fine adjustment circuit,and a central processing unit adapted to adjust the zero-point of saidweighing device by receiving a no-load weight signal outputted from saidweighing device and controlling the output signals from said rough andfine adjustment circuits.
 2. The zero-point adjustment unit of claim 1wherein said rough adjustment circuit includes a first digital-to-analogconverter for rough zero-point adjustment and a first subtracter forrough zero-point adjustment, and said fine adjustment circuit includes asecond digital-to-analog converter for fine zero-point adjustment and asecond subtracter for fine zero-point adjustment.
 3. The zero-pointadjustment unit of claim 2 wherein said rough and fine adjustmentcircuits include an analog-to-digital converter, said first subtracterserves to receive an output signal from said first digital-to-analogconverter and an analog no-load signal from said weighing device and tocorrespondingly output a first difference signal, and said secondsubtracter serves to receive an output signal from said seconddigital-to-analog converter and an output signal from said firstsubtracter and to correspondingly output a second difference signal tosaid analog-to-digital converter.